If my memory is correct, both ends of the O2 sensor are business ends. The 02 sensor works on a chemical reaction of comparing the oxygen content of the air inside the exhaust pipe against a reference from outside the exhaust pipe. In theory, if you manage to get some oil past the metal shield on the outside of the sensor (which isn't air-tight), then you could have contaminated the chemical probe.

If you do find a 3-wire Bosch 02 sensor for $30, please post a souce for us. I'll be interested in buying a few.

God bless,
Fitz Fitzgerald.
--
'87 Blue 245, NA 223K